Densitometers can measure the passage of light through a transparent or semitransparent material. The measured density of a measurable substance is typically determined by measuring a decrease in the amount of light which passes through the measurable substance, the measurement may be related to the absorption of light of the measurable substance.
Most densitometers include a light source, often a laser, aimed at a photoelectric cell, with the measurable substance between the light source and the photoelectric cell. The densitometer determines the density of the measurable substance by analyzing the attenuation of light from the light source that has passed through the substance, and comparing that value with a known reference value.
Densitometers can be either transmission densitometers or reflection densitometers. Transmission densitometry instruments typically measure how transparent a substance is to visible light or other electromagnetic radiation. Reflection densitometry devices measure the amount of reflected signal, typically light or other electromagnetic radiation, of a sample. Densitometers are used in many industries as tools to measure the optical density of materials, i.e., liquids, and to provide quality assurances of a particular liquid, including foodstuffs, medications, or ink for printers.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.